1. Field of the Invention
The present invention relates to a disk brake apparatus and, specifically, to a disk brake apparatus which includes a piston for pushing a friction pad in accordance with a hydraulic pressure, an adjuster for automatically adjusting a clearance between the friction pad and a disk rotor, and a parking brake for pushing the piston through the adjuster by a ball ramp type thrust conversion mechanism.
2. Description of Related Art
As disk brake apparatuses for use in a four-wheel drive car, there are known a disk brake apparatus with a parking brake which includes a hydraulic pressure type operation mechanism using a brake pedal and a mechanical type operation mechanism pulled and operated by a hand lever or a foot pedal.
In this disk brake apparatus with a parking brake, generally, a piston constituting a hydraulic pressure type operation mechanism is disposed on a leading end opening side of a cylinder hole formed in a caliper body, an adjuster which includes an adjust nut and an adjust bolt is disposed on the rear surface side of this piston and a thrust conversion mechanism which constitutes a mechanical type operation mechanism is disposed on the bottom side of the cylinder hole.
As the thrust conversion mechanism, conventionally, there is widely used a ball ramp type thrust conversion mechanism. This conventional ball ramp type thrust conversion mechanism is structured in the following manner.
That is, a fixed side cam plate and a drive side cam plate, which respectively include a ramp groove for accommodating a cam bearing therein, are disposed opposed to each other; the drive side cam plate is rotated by the operation of the parking brake. Due to this rotation, by a cam action generated between the ramp groove and cam bearing, thrust force which can move a piston toward a disk rotor is generated and by this thrust force, the piston is moved in the direction of the disk rotor through the adjuster to press the friction pad against the disk rotor, thereby obtaining a braking force.
There is also known a disk brake apparatus in which a substantially cylindrical housing which accommodates the fixed side cam plate, drive side cam plate, a thrust transmission plate and a cam spring for energizing the thrust transmission plate in the direction of the drive side cam plate, and which is disposed on a bottom side of the cylinder hole, thereby enhancing the efficiency of the operation to assembly the disk brake apparatus (for example, see Japanese Patent Unexamined Publication JP-A-2000-320588).
However, in the above-mentioned disk brake apparatus, it takes much time and troublesome to discharge air mixed in hydraulic fluid charged into the cylinder hole and, especially, in the housing, it is difficult to discharge the air of the hydraulic fluid therefrom, resulting in the poor efficiency of the operation of the disk brake apparatus.